Magnetic flowmeters (or mag meters) measure flow by application of Faraday's Law, an electromagnetic effect. The magnetic flowmeter energizes one or more coils by passing an excitation current through field windings which generates a magnetic field across an electrically isolated, conductive process flow. An electromotive force (EMF) is generated by the flowing process fluid crossing through the magnetic field; this induced voltage (potential) both across the fluid and with respect to the rest of the process fluid can readily be measured by one or more conductive electrodes that contact the flowing process fluid. Alternatively, some magnetic flowmeters employ capacitive coupling between the electrodes and the process fluids such that the potential can be measured without direct electrical connection to the process. The volumetric flow is proportional to the flow velocity and the cross-sectional area of the flowtube. As the flow velocity is directly proportional to the electrode voltage potential (EV), the electrode voltage potential (EV) is directly proportional to the induced magnetic field strength (B), and the induced magnetic field strength is assumed to be proportional to the applied magnetic field (H), which is directly linked to the magnitude of the excitation current, a direct correlation is provided between measured electrode voltage potential and indicated volumetric flow.
Magnetic flowmeters are useful in a variety of conductive and semi-conductive fluid flow measurement environments. In particular, the flow of water-based fluids, ionic solutions and other conducting fluids can all be measured using magnetic flowmeters. Thus, magnetic flowmeters can be found in water treatment facilities, beverage and hygienic food production, chemical processing, high purity pharmaceutical manufacturing, as well as hazardous and corrosive processing facilities. Magnetic flowmeters are often employed in the hydrocarbon fuel industry which sometimes employs hydraulic fracturing techniques using abrasive and corrosive slurries.